What would be the easiest way to UV map a complex object?
Model your own UV Map

This technique allows precision control over the geometry of your layout by unwrapping from a Shape Key pose.

"Project From View" allows anything we are looking at in the 3D Viewport to be stamped into 2D space (a UV layout). The trouble is that even if we can get a good projection angle there are usually some pieces of geometry on the other side of the model that will overlap in 2D. The solution I came up with is to model exactly what gets projected. Luckily UV projection takes Shape Keys into account, and we can reseal a ripped mesh without doing harm to the UV Map.

While it is powerful, this approach is not the most appropriate solution for every case. It is best to become familiar with the traditional UV unwrapping methods because often those will suffice. For example, if you have a cylindrical shape then Cylinder Projection is probably the best approach. The following technique is for getting at the hard-to-reach places and it can spare you many UV mapping headaches. It seems the standard unwrapping techniques weren't enough in your case, so hopefully this will help you.

Save a backup copy of your mesh and let's begin.

1. Rip it

Select the edges where you would normally mark seams and instead rip the vertices V, then press Esc to snap them back into place.

You can then select any individual piece or "island" by selecting a single part of the geometry and then Selecting Linked (CtrlL).



Another way is to mark all of your seams first (CtrlE > "Mark Seam"), then select a face and choose Select Linked (CtrlL). The selection will by default be delimited by the seams. (This must be done using Face Selection, not Vertex or Edge Selection.) Then choose Select > Select Boundary Loop, and Rip (V).

2. Add shape keys

From Object Mode, in the Mesh Context, add a shape key for the base mesh, then a second one. Label the second one "UV" and make sure it's selected before proceeding.



3. Flatten it out

In Edit Mode, Edit your model to be flat and fit nicely within a square area. Actually, it doesn't need to be totally flat as long as it appears flat from the projected view angle - that is, no faces overlapping. I found it easier to manage flattening each piece as I finished it. To flatten simply scale along the axis you will project along. In my example it would be SYNum 0. Of course it's not just a matter of flattening, but modeling it into a shape with no overlap and then flattening.

The goal is to end up with a mesh that is flat in its "UV" Shape Key:



This step is a modeling process that will vary from model to model. Here are a few of the tools you will probably find useful during this process:


Select Linked CtrlL - Selects all connected geometry. Use it to select each "island".
Hide Unselected ShiftH - Hides everything except what you have selected.
Unhide AltH - Puts hidden geometry back in view.
Proportional Editing (Connected) AltO - Influences the verts around your selection too.
Shrink/Fatten AltS - Pushes out or pulls in selected geometry relative to the Pivot Point.
Edge Slide GG - Slides an edge loop toward or away from neighboring edge loops.


Remember: Do not add or remove any geometry. When editing a Shape Key pose you are only pushing verts around, not adding, deleting, welding, or extruding. Reshape the geometry by moving positions of the vertices, that's all.

Make sure face normals are pointing toward the direction you will be looking from when you project your UV layout. Do not simply flip the normals. Instead rotate the piece to be facing the correct direction - outer part facing forward.

An animation showing the shape key transition of a model from 3D to 2D for UV unwrapping:



For hard surface modeling especially, such as with the model in your .blend, you will want there to be minimal stretching. So whenever possible, instead of stretching, rotate with the 3D Cursor as your Pivot Point.



Also, for hard surface modeling you have the luxury of separating large mesh objects into smaller, more manageable ones. Separate in places where you can hide the seams, or where seams occur anyway, such as where panels connect. You can then make a UV Map for each object. Each object can have a maximum of 8 UV Maps.

4. Unwrap

Method 1: The simple way

Put your 3D Viewport in Orthographic view. Look at your flattened mesh straight on and Unwrap (U) using > "Project From View". Scale it to fit nicely within the square grid of the the UV/Image Editor.

Method 2: Unwrapping for symmetrical objects

One limitation with Shape Keys is that modifiers cannot be applied while the mesh object is using them. So if your mesh has symmetry generated by a Mirror Modifier, project onto just one half of the UV area. To get the projection perfectly centered, set your Camera to Orthographic, make the dimensions square, and make sure the camera is directly aligned with your object. Enter Camera View (Num 0). The unwrapping will use the camera's bounds as the UV Map bounds. Press U and choose "Project From View".



5. Adjustments

At this stage you can refine the UV Map.
You can grab, rotate, and scale the UV islands to pack them together more efficiently. You may want to check your UV density by creating a UV Grid and nudging the verts of the UV Map so that the size of the texture becomes uniform over the model.

Do an incremental Save As, because next comes a destructive edit.

6. Piece it back together

From Object Mode, delete the shape keys. First the "UV" shape key, then the "Basis" shape key.

From Edit Mode, select the entire mesh, press W, and select Remove Doubles. The vertices we ripped before are now mended.

Applying the Mirror Modifier on symmetrical objects

If your mesh object is using a Mirror Modifier you can leave it on for now in case you want to keep your options open. But if or when you would like to texture the left and right sides differently you will need to apply the Mirror Modifier. (Note that if you plan to use a normal map the two sides must be unique in order to avoid shading problems; the normal map cannot simply be mirrored the way a diffuse texture can.)

Apply the modifier from Object Mode, then from Edit Mode select the newly generated half of your model, including the center vertices. The selected vertices will show up in the UV/Image Editor, however they are lying directly under the vertices that were originally projected. To flip them over to the opposite side, place the 2D Cursor in the center of the UV area on the X axis, set the Pivot Point to be the 2D Cursor, then scale -1 along the X axis.



And that's it, now you have a UV Map that looks exactly the way you want!